Intraluminal devices have become important in the diagnoses and treatment of a variety of medical conditions ranging from conditions associated with the digestive system to conditions related to the cardiocirculatory system. Current intraluminal sensing and therapeutic devices suffer from various disadvantages due to a lack of sophistication related to the sensing, imaging, and therapeutic functions. In some cases, such lack of sophistication resides in the fact that many such devices are configured with passive circuitry. Active integrated circuits utilizing multifunctional operative devices offer a variety sophisticated sensing, imaging, and therapeutic functions, including (but not limited to) pressure sensing, light imaging, and drug delivery. In the case where intraluminal devices have such active integrated circuits, such devices suffer from other disadvantages not the least of which is that such devices are unable to achieve direct contact with the part of the body being measured. The inability to achieve direct contact of such devices is attributable to the rigid nature of the operative devices and accompanying circuitry. This rigidity prevents devices from coming into full contact with soft, pliable, curved, and/or irregularly shaped tissue, which compromises accuracy of measurements.
By way of a non-limiting example, one such area where a need exists to obtain better contact and thus accuracy is in the area of analyzing arterial plaque deposits. Plaque deposits in the arterial lumen are widely recognized as a common cause of myocardial infarction, unstable angina, and even death. Plaques found inside the arterial lumen are classified as ‘vulnerable’ or ‘stable.’ These two types of plaque have significantly different compositions that give rise to variations in electrical, thermal, chemical, and material properties. Vulnerable plaque consists of a lipid core containing large amounts of cholesterol deposits, inflamed cells (macrophages), low levels of collagen and other matrix proteins. The collagen and associated fibrous proteins are found as a thin surface layer, encapsulating all of the other structural components. Based on size and the effects of shear stress exerted by the flow of blood, the enclosure formed by the thin fibrous caps is susceptible to mechanical rupture. The rupture and subsequent release of the deposits internal to the plaque is a key mechanism underlying thrombosis and myocardial infarctions.
In contrast, stable plaque is much less susceptible to rupture and thus is far less dangerous. Stable plaques have a significantly more robust outer shell, consisting of a thick fibrous cap. Although stable plaques can cause significant stenosis that may require intervention, the effect of arterial occlusion is much less harmful than the rupture of vulnerable plaque. It is important to note that the vulnerable plaque typically form a narrowing of less than 50%, suggesting that the deleterious effects of a vulnerable plaque cannot be predicted based on the extent of occlusion alone. Moreover, it is difficult to distinguish between vulnerable and stable plaque based purely on extracorporeal imaging techniques.
One direct way to detect the presence of vulnerable plaque is through temperature and pressure sensing near the plaque site, since plaque has non-uniform surface contours and because there is a significant difference in the temperature of vulnerable plaque compared to that of the normal lumen and stable angina. But current temperature sensors are fabricated on rigid supports and embedded within the catheter body. One such sensor is located at the center of the lumen in the catheter. This design requires compensation for the distance separating the temperature sensor from the plaque wall. Adjustments in temperature recordings are made based on a displacement sensor that senses the distance between the plaque wall and the catheter within the lumen. Although this type of device can theoretically estimate the temperature at the plaque, complications and errors can arise.